Influence of pipe material and surfaces on sulfide related odor and corrosion in sewers

Hydrogen sulfide oxidation on sewer pipe surfaces was investigated in a pilot scale experimental setup. The experiments were aimed at replicating conditions in a gravity sewer located immediately downstream of a force main where sulfide related concrete corrosion and odor is often observed. During the experiments, hydrogen sulfide gas was injected intermittently into the headspace of partially filled concrete and plastic (PVC and HDPE) sewer pipes in concentrations of approximately 1000 ppm_v. Between each injection, the hydrogen sulfide concentration was monitored while it decreased because of adsorption and subsequent oxidation on the pipe surfaces. The experiments showed that the rate of hydrogen sulfide oxidation was approximately two orders of magnitude faster on the concrete pipe surfaces than on the plastic pipe surfaces. Removal of the layer of reaction (corrosion) products from the concrete pipes was found to reduce the rate of hydrogen sulfide oxidation significantly. However, the rate of sulfide oxidation was restored to its background level within 10-20 days. A similar treatment had no observable effect on hydrogen sulfide removal in the plastic pipe reactors. The experimental results were used to model hydrogen sulfide oxidation under field conditions. This showed that the gas-phase hydrogen sulfide concentration in concrete sewers would typically amount to a few percent of the equilibrium concentration calculated from Henry's law. In the plastic pipe sewers, significantly higher concentrations were predicted because of the slower adsorption and oxidation kinetics on such surfaces.     

Electrokinetically deposited coating for increasing the service life of partially deteriorated concrete sewers

Microbiological induced corrosion (MIC) is a leading deterioration mechanism in concrete wastewater conveyance systems. The work reported herein focuses on breaking the MIC cycle by preventing colonization of the bacteria responsible for converting hydrogen sulfide to sulfuric acid. Electrokinetics was used to drive an antimicrobial agent (cuprous oxide) into the porous wall surface of a pre-cast concrete pipe. An electric potential difference, applied between the steel reinforcement embedded in the concrete and a copper electrode placed in the coating solution, provides the driving force to the copper ions. Atomic absorption tests performed on the coated specimens were used to determine the percentage of cuprous oxide that penetrated the porous surface and migrated into the hardened concrete matrix. A pilot study conducted on three mock pipe specimens demonstrated that the process is effective on partially corroded and non-corroded pipes. Test data also revealed that the amount of copper that migrated into the concrete matrix is time dependent. Based on preliminary test results a treatment procedure was designed and implemented on a 380 mm diameter commercial pre-cast concrete pipe. The data suggest that the method could be deployed to “immune” new and partially deteriorated steel reinforced concrete pipes against MIC.     

内衬HDPE片材大口径钢筋混凝土排水管检测试验初探

基于工程实际要求,对内衬高密度聚乙烯(HDPE)片材化学物理性能及内衬HDPE片材钢筋混凝土管节进行了试验研究,包括内衬HDPE单键和多键的抗拉拔试验、管节接头抗内水压和外水压试验、HDPE片材覆贴接头抗外水压试验、外压荷载试验,可为HDPE片材在钢筋混凝土排水管中的应用和推广提供参考。     

Assessment of hydrogen sulphide corrosion of cementitious sewer pipes: a case study

A study was conducted to assess hydrogen sulphide corrosion in cementitious sewer pipes and concrete culverts existing in the four largest coastal cities and their environs in Lebanon. Significant factors and parameters affecting H₂S corrosion were measured both in the field and in the laboratory. All collected samples were obtained from existing sewer networks that are more than 30 years old. Pipe samples obtained from these locations did not exhibit any corrosion indicators. Alkalinity measurements indicated the occurrence of mild corrosion leading to neutralization of concrete (calcareous aggregates) particularly at the pipe crown. Testing for the sulphate content of the samples did not reveal a clear trend as to the distribution of sulphates along the pipe circumference. Parameters of the existing sewer networks upstream of sample sites, along with survey data obtained from the field were introduced into commercial software for the evaluation of sulphide generation and annual corrosion rates. The results indicated that hydrogen sulphide will only be generated in negligible quantities under the prevailing environmental conditions, and hence H₂S corrosion could proceed, but at very slow rates.     

Uncertainties associated with laser profiling of concrete sewer pipes for the quantification of the interior geometry

Structural strength and hydraulic capacity are two essential parameters in the assessment of the need for sewer rehabilitation. Especially concrete pipes suffer from loss of wall thickness due to biochemical corrosion and, consequently, a decreasing structural strength along with an increase of hydraulic roughness. Unfortunately, routinely used visual inspection methods do not allow a quantification of the internal pipe geometry which would enable not only detecting but also quantifying the progress of biochemical corrosion. Advances in laser technology and digital cameras theoretically allow a cost-effective application of laser profilers to measure the interior geometry of sewer pipes. An analysis of associated uncertainties revealed that the position and alignment of the laser are the main source of measurement errors. A full-scale laboratory set-up demonstrated, based on tests on a new and an 89 years old corroded sewer pipe, that laser scanning is indeed capable of measuring the interior geometry accurately enough to determine wall thickness losses for corroded pipes, provided that the position and alignment of the laser and camera are accounted for. The obtained accuracy, however, was not enough to quantify the hydraulic roughness.     

Electrochemical sulfide removal from synthetic and real domestic wastewater at high current densities

Hydrogen sulfide generation is the key cause of sewer pipe corrosion, one of the major issues in water infrastructure. Current abatement strategies typically involve addition of various types of chemicals to the wastewater, which incurs large operational costs. The transport, storage and application of these chemicals also constitute occupational and safety hazards. In this study, we investigated high rate electrochemical oxidation of sulfide at Ir/Ta mixed metal oxide (MMO) coated titanium electrodes as a means to remove sulfide from wastewater. Both synthetic and real wastewaters were used in the experiments. Electrochemical sulfide oxidation by means of indirect oxidation with in-situ produced oxygen appeared to be the main reaction mechanism at Ir/Ta MMO coated titanium electrodes. The maximum obtained sulfide removal rate was 11.8 ± 1.7 g S m⁻² projected anode surface h⁻¹ using domestic wastewater at sulfide concentrations of ≥30 mg L⁻¹ or higher. The final products of the oxidation were sulfate, thiosulfate and elemental sulfur. Chloride and acetate concentrations did not entail differences in sulfide removal, nor were the latter two components affected by the electrochemical oxidation. Hence, the use of electrodes to generate oxygen in sewer systems may constitute a promising method for reagent-free removal of sulfide from wastewater.     

Long-term field test of an electrochemical method for sulfide removal from sewage

Corrosion caused by hydrogen sulfide leads to significant costs for the rehabilitation or replacement of corroded sewer pipes. Conventional methods to prevent sewer corrosion normally involve the dosing of significant amounts of chemicals with the associated transport and storage costs as well as considerable maintenance and control requirement. Recently, a novel chemical free method for sulfide abatement based on electrochemical sulfide oxidation was shown to be highly effective for the removal of sulfide from synthetic and real sewage. Here, we report on the electrochemical removal of sulfide using Ta/Ir and Pt/Ir coated titanium electrodes under simulated sewer conditions during field trials. The results showed that sulfide can successfully be removed to levels below the normal target value at the end of a simulated rising main (i.e. <1 mg/L). A coulombic efficiency for dissolved oxygen generation of ∼60% was obtained and was independent of the current density. Scaling of the electrode and the membrane was observed in the cathode compartment and as a result the cell potentials increased over time. The cathode potentials returned to their original potential after switching the polarity every two days, but a more frequent switching would be needed to reduce the energy requirements of the system. Accelerated lifetime experiments indicated that a lifetime of 6.0 ± 1.9 years can be expected under polarity switching conditions at a pH of 14 and significantly longer at lower pH values. As operating the system without switching simplifies construction as well as operation, the choice whether to switch or not will in practice depend on operational cost (higher/lower energy) versus capital cost (reactor and peripherals). Irrespective of the approach, our study demonstrates that electrochemical sulfide control in sewer systems may be an attractive new option.     

Relating the structural strength of concrete sewer pipes and material properties retrieved from core samples

Drill core samples are taken in practice for an analysis of the material characteristics of concrete pipes in order to improve the quality of the decision-making on rehabilitation actions. Earlier research has demonstrated that core sampling is associated with a significant uncertainty. In this paper, the results of core samples are compared with the results of full-scale pipe cracking lab experiments. It is shown that the concrete of deteriorated sewer pipes shows a significant variability in material characteristics. Further it is shown that the formation of ettringite due to biochemical sulphuric corrosion is not necessarily limited to the crown of the pipe and also degradation of pipe material, measured by the carbonation depth, is occurring at the inside and outside of the pipe. It is concluded that tensile splitting strength and the carbonation depth are the two material property parameters of core sampling with a sufficiently high correlation (R² > .90) with the structural strength of the pipe. The thickness of the remaining ‘healthy’ concrete material is the optimal parameter, as this requires the smallest sampling size.     

小口径混凝土排水管密封胶圈的设计研究

为解决实际工程中小口径混凝土排水管的连接质量问题,通过排水管对接连接和内水压力试验,建立了不同硬度、不同压缩率密封胶圈与排水管对接安装难易程度及质量的关系,并针对实际工程,提出了合理的改进意见,以期为提高小口径混凝土排水管的对接安装质量提供参考。     

超大直径钢筋混凝土顶管在排水工程中的应用

本文叙述了国内外顶管技术的发展历史,简要介绍了国内大直径钢筋混凝土顶管在排水工程中的应用与实践,详细分析和归纳了上海南线污水输送管线两条DN4000钢筋混凝土顶管平行顶进的设计和施工技术,为今后同类工程的推广应用和发展提供参考和借鉴。     

西江引水工程预应力钢筒混凝土管的防腐措施

广州市西江引水工程输水干线主管材采用预应力钢筒混凝土管(PCCP)。为确保管道运行安全,采取提高水泥砂浆保护层质量、环氧煤沥青涂料外防腐、环氧饮水舱漆内防腐和聚硫密封膏接口密封防腐措施,提高了PCCP管的防腐能力,对类似工程具有借鉴意义。     

Geochemical contamination of urban water by concrete stormwater infrastructure: applying an epoxy resin coating as a control treatment

Urban drainage systems that use concrete gutters, pits and pipes have been adopted worldwide by drainage engineers. This study tested the hypothesis that treating a concrete pipe with a coating of epoxy resin is an effective method to reduce the concrete mineral leaching and associated contamination of water carried within the pipe. Four 20 litre samples of rainwater were individually circulated through the untreated and epoxy treated portions of the pipe for 100 minutes. After recirculation through the untreated portion of the pipe pH increased by almost two units, electrical conductivity doubled and there were significant increases in bicarbonate, calcium and other ions. In contrast, rainwater circulated through the epoxy treated portion of the pipe showed a minimal pH increase (0.32 pH units) but no other significant increases in any other water chemistry attributes. The epoxy resin greatly reduced mineral contamination of recirculated water, supporting the hypothesis.     

A method to consider replaced pipes in modeling of sewer pipe deterioration

Statistical models that predict the deterioration of sewer pipes are useful for planning financial resources required for sewer renewal. Usually, data that are available to calibrate these models solely concern pipes that are still in place, leading to underestimated deterioration rates. A new method is proposed to consider possible past replacement of pipes in the statistical modeling of their deterioration. The proposed method considers the aging of pipes, simulated with a Cox model, and their probability to be replaced separately. Application to a synthetic sewer network, for which it was assumed that information regarding all pipe replacements over the lifetime of the network was available, showed that the proposed method allows for improved predictions of the sewer deterioration model, when compared to predictions of a model calibrated without considering the information about replaced pipes.     

Surface neutralization and H₂S oxidation at early stages of sewer corrosion: influence of temperature, relative humidity and H₂S concentration

While the involvement of a range of environmental factors in sewer corrosion is known, a comprehensive understanding of the processes involved and the exact role of individual environmental factors in sewer corrosion is still lacking. The corrosion of concrete in sewer systems is reported to be initiated through chemical reactions (involving H₂S and CO₂) that lower the surface pH to a level then conducive for biological activity. However, the specific influence of environmental variables, such as H₂S level, temperature, and relative humidity etc. remains unclear; although, they are expected to control these initial surface reactions of the concrete sewer pipe. We examined changes in the surface chemistry of concrete during the early stages of corrosion by exposing concrete coupons to thirty-six independent conditions in well-controlled laboratory chambers that simulated conditions typically found in various sewer environments across Australia. The conditions employed were combinations of six H₂S levels, three gas-phase temperatures and two relative humidity levels. Our results indicate that the role of CO₂ on initial surface pH reduction is insignificant when compared to the influence of H₂S. Within the first 12 months, a decrease in surface pH by 4.8 units was observed for coupons exposed to 30 °C and 50 ppm H₂S, while significantly lower pH reductions of 3.5 and 1.8 units were detected for coupons exposed to 25 °C and 18 °C respectively, and 50 ppm H₂S. Elemental sulphur was found to be the major oxidation product of H₂S and elevated concentrations were detected at the higher levels of H₂S, temperature and relative humidity. More significantly, the data obtained from the controlled chamber experiments correlated with those obtained from the field-exposed coupons. Hence, these findings can be extended to real sewer corrosion processes.     

Chemical and biological technologies for hydrogen sulfide emission control in sewer systems: a review

Biogenic corrosion of sewers represents a cost of about 10% of total sewage treatment cost in Flanders (Belgium) and is further increasing. In the past, research has resulted in a number of prevention methods, such as injection of air, oxygen, H(2)O(2), NaClO, FeCl(3) and FeSO(4). The possibility of biological oxidation of sulfide using nitrate as the electron acceptor has also been explored in sewer systems. However, all of these methods have a problem with the high cost (euro 1.9-7.2 kg(-1)S removal). In this review, new approaches for hydrogen sulfide emission control in sewer systems are discussed. The control of hydrogen sulfide emission by using a microbial fuel cell (MFC) can be cost-effective while the BOD is removed partially. The use of phages that target sulfate-reducing bacteria (SRB) can possibly inhibit sulfide formation. Novel inhibitors, such as slow release solid-phase oxygen (MgO(2)/CaO(2)) and formaldehyde, warrant further study to control hydrogen sulfide emission in sewer systems.     

Evaluating a polymer concrete coating for protecting non-metallic underground facilities from sulfuric acid attack

Deteriorating underground facilities built with cement concrete and clay bricks require rapid in situ rehabilitation, and using coating as a corrosion protectant is one method currently being adopted. The performance of a polymer concrete coating was evaluated using a combination of full-scale and laboratory tests. The polyester-based polymer concrete coating had a density of 1.75 g/cm³ (109 lb/ft³) and hardness in the range 38–45 (Barcol hardness). A full-scale test on coating applicability and performance on the concrete substrate was performed under an external hydrostatic pressure of over 103 kPa (15 psi) of water, simulating the groundwater condition. Coated concrete cylinders and clay bricks with holidays (pinholes) were used to study the chemical resistance of the coating under acidic environments to represent the worst sewer and accelerated test conditions (ASTM G 20). Bond strength between the coating and the concrete/clay brick substrates were determined using the modified ASTM D 4541 test. The performance of the polymer concrete coating material was studied for over 3 years. The polymer concrete coating was applied with ease on dry and wet concrete surfaces. Test results showed that the polymer concrete coating had good bond strength with clay bricks and wet concrete surface. No failure was observed in 3 years with coated clay bricks. The coating extended the lifetime of dry and wet concrete by a factor of 29 and 71, respectively. The weight change of coated concrete was modeled using a film model.     

Prediction models for sewer infrastructure utilizing rule-based simulation

Management of infrastructure projects is becoming increasingly challenging due to inherent uncertainties. The most effeective way to deal with uncertainty is to collect supplementary information and knowledge. When expensive or infeasible, quantification of uncertainty may be performed using analytical or simulation techniques. The City of Edmonton, Canada has approximately 4600 km of sewer pipes in the combined, sanitary, and storm sewer local systems with uncertainty issues related to deterioration. The City has taken a proactive approach with respect to sewer rehabilitation, as it is more cost-effeective to repair a defective pipe prior to failure rather than after a collapse. This article demonstrates an approach for predicting the condition of a sewer pipe and the related cost of rehabilitation, given the limited data. Three models are described in this article that are developed to assist the City of Edmonton to effeectively plan maintenance expenditure. Each model uses a combination of rule-based simulation and probability analysis to assist in the planning of future expenditures for sewer maintenance, thereby producing an invaluable planning tool.     

A different approach for predicting H(2)S((g)) emission rates in gravity sewers

All detrimental phenomena (mal odors, metal corrosion, concrete disintegration, health hazard) associated with hydrogen sulfide in gravity sewers depend on the rate of H(2)S emission from the aqueous phase to the gas phase of the pipe. In this paper a different approach for predicting H(2)S((g)) emission rates from gravity sewers is presented, using concepts adapted from mixing theory. The mean velocity gradient (G=gamma SV/micro; S is the slope, V the mean velocity), representing mixing conditions in gravity flow, was used to quantify the rate of H(2)S((g)) emission in part-full gravity sewers. Based on this approach an emission equation was developed. The equation was verified and calibrated by performing 20 experiments in a 27-m gravity-flow experimental-sewer (D=0.16 m) at various hydraulic conditions. Results indicate a clear dependency of the sulfide stripping-rate on G(1) (R(2)=0.94) with the following overall emission equation: where S(T) is the total sulfide concentration in the aqueous phase, mg/L; w the flow surface width, m; A(cs) the cross-sectional area, m(2); T the temperature, degrees C; K(H) the Henry's constant, molL(-1)atm(-1); and P(pH2S) the partial pressure of H(2)S((g)) in the sewer atmosphere, atm.     

市政道路排水管材选用探讨

根据我国混凝土和钢筋混凝土排水管材的现行标准 ( GB1 1 836 -* * ) ,并结合市政道路排水工程的实际情况 ,对排水管材标准的选用进行了探讨。     

Segmentation of buried concrete pipe images

The enormity of the problem of deteriorating pipeline infrastructure is widely apparent. Since a complete rebuilding of the piping system is not financially realistic, municipal and utility operators require the ability to monitor the condition of buried pipes. Thus, reliable pipeline assessment and management tools are necessary to develop long term cost effective maintenance, repair, and rehabilitation programs. In this paper a simple, robust and efficient image segmentation algorithm for the automated analysis of scanned underground pipe images is presented. The algorithm consists of image pre-processing followed by a sequence of morphological operations to accurately segment pipe cracks, holes, joints, laterals, and collapsed surfaces, a crucial step in the classification of defects in underground pipes. The proposed approach can be completely automated and has been tested on five hundred scanned images of buried concrete sewer pipes from major cities in North America.